Meeting Rooms II - Walkthrough

Meetings: [[0,30], [5,10], [15,20]]. Events: ($0$,+1), ($5$,+1), ($10$,-1), ($15$,+1), ($20$,-1), ($30$,-1). Sorted: ($0$,+1), ($5$,+1), ($10$,-1), ($15$,+1), ($20$,-1), ($30$,-1). Running count: $0$ -> $1$ -> $2$ -> $1$ -> $2$ -> $1$ -> $0$. Maximum: $2$. So $2$ rooms are needed.

The peak happens when meetings [0,30] and [5,10] overlap, and again when [0,30] and [15,20] overlap. The count tracks how many meetings are active at each event time. The maximum count is your answer. This approach simulates the timeline.